Due to the relatively short duration during which platelets can be preserved in a viable state, Federal regulations require that platelets be stored no more than three days at 22.degree. C. before use. It is known that pH commonly falls during storage of blood platelets at 22.degree. C. When the pH reaches 6.0, morphological changes occur in the platelets and viability is lost.
Murphy and Gardner, Blood, 46, 209-218 (1975) disclose that when containers constructed of polyvinylchloride are used for storage of platelet concentrations, at 22.degree. C., pH often falls to such low levels (pH &lt;6.0) that viability is lost. They disclose that far lesser degrees of pH fall are observed in bags constructed of polyethylene. From their study of conditions necessary to maintain viability during 3 days storage these authors conclude that (1) pH falls because of the generation of lactic acid by platelet glycolysis and, under some circumstances, the retention of CO.sub.2 ; (2) the rate of pH fall is roughly proportional to the platelet count; (3) polyethylene is more permeable to gases, thereby allowing CO.sub.2 escape from and easier O.sub.2 entry into the stored platelet concentrates; higher O.sub.2 tensions suppress glycolysis by the Pasteur effect; (4) adequate agitation and container size are critical if the beneficial effect of polyethylene is to be obtained; (5) in general, platelets stored in polyethylene containers have excellent viability in vivo although CO.sub.2 escape can result in elevations in pH which are deleterious; (6) storage in a 10% CO.sub.2 atmosphere prevents these deleterious pH elevations without otherwise impairing platelet viability; and (7) results similar to those achieved with polyethylene can be achieved with polyvinyl chloride if it is made thinner to allow easier penetration of gases.
U.S. Pat. No. 4,140,162, issued to Gajewski et al on Feb. 20, 1979, discloses a clear, autoclavable, blow-moldable plastic formulation for medical and other uses comprising a two, or optionally three, component system including (1) a polyolefin consisting of propylene units as a first component, (2) a block copolymer having thermoplastic rubber characteristics with a central block of ethylenebutylene copolymer and terminal blocks of polystyrene, and (3) an optional third ingredient comprising a softening agent of polyethylene or poly(ethylenevinyl acetate). Blood bags made from the formulation are also disclosed. U.S. Pat. No. 4,222,379 indicates that this formulation exhibits good carbon dioxide transfer characteristics and is suitable for use as transfer bags for storing platelets.
U.S. Pat. No. 4,222,379, issued to Smith on Sept. 16, 1980, discloses a multiple blood bag system which comprises a first bag, a second bag, and conduit means providing sealed flow communication between them. The first bag is made of a plastic material which comprises a different polymer entity from that of the second bag, and the polymer entity of the first bag exhibits the characteristic of suppressing hemolysis of blood cells on long term storage. The patent further discloses that the first (donor) bag may be made of a transparent, flexible, sterilizable material which contains a blood-extractable plasticizer whereas the second (transfer) bag may be made of a translucent, flexible, sterilizable material which is free of blood-extractable plasticizer and may be a material which permits an increased diffusion rate of carbon dioxide during platelet storage so that the pH decrease of the platelets during storage is reduced.
A platelet storage container which permits increased storage time during which viability can be maintained would present definite advantages to the medical profession. Hospitals would be less susceptible to fluctuations in supply versus demand and would suffer less during long weekends when heretofore, because of Federal regulations, the platelet supply quite often had to be nearly depleted before the weekend ended. The provision of such a container from relatively thin material using easy fabrication techniques is a desirable goal offering functional and commercial benefits.